POS0566 SURVIVAL ON TREATMENT AFTER SWITCHING TO A BIOSIMILAR: POPULATION-BASED EVIDENCE FROM A NATURAL EXPERIMENT DUE TO A POLICY CHANGE
Authors: D. Lacaille, J. A. Aviña-Zubieta, Y. Zheng, N. Lu, H. Xie
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> In the province of British Columbia (BC), Canada, a health policy implemented in July 2017 mandated that all new anti-TNF prescriptions for which a biosimilar exists, i.e., etanercept and infliximab at the time, be dispensed a biosimilar rather than the originator, for universal cost coverage by BC PharmaCare. In May-December 2019, a further policy mandated that current users of anti-TNF agents be switched to the corresponding biosimilar. <h3>Objectives</h3> The objective of this study is to compare the survival on treatment (as a surrogate marker of effectiveness and safety), between biosimilar switchers vs. users of originator Anti-TNF for inflammatory arthritis, after and before the health policy change. <h3>Methods</h3> Study Cohort: Using administrative data and validated definitions, we identified etanercept and infliximab users with rheumatoid arthritis (RA), psoriasis or psoriatic arthritis (Pso/PsA), or ankylosing spondylitis and other spondyloarthritis (SpA). Biosimilar switchers were current biologic users who switched to the corresponding biosimilar during the period of May to December 2019. Historical controls were randomly selected from all new users of originator etanercept and infliximab before July 2017, matched to biosimilar switchers on sex, previous number of biologics used, and disease. Controls were assigned an index date such that duration of originator anti-TNF therapy was the same at switching/index date for switchers and controls. Outcomes: Discontinuation was defined as no prescription renewal for at least 6 months. Statistical method: We followed patients from switching/index date to discontinuation, or for two yearsor until last health care utilization (if moving out-of-province), or end date of the follow-up (April 30, 2019 for originators, and December 31, 2021 for switchers), whichever occurred first. Weighted Cox proportional hazards models with propensity score overlap weighting estimated the HR of discontinuing anti-TNF agents for controls and switchers, adjusting for duration of of anti-TNF agent use at switch/index date, age, sex, socio-economic status (low income subsidy), rural vs urban residence, health authority, arthritis type, number of prior biologic agents, comorbidities, and other IA drugs used (MTX, non MTX DMARDs and glucocorticosteroids), all measured at time of switching/index date. <h3>Results</h3> A total of 1631 biosimilar switchers (1402 eternercept; 229 infliximab) were included in this study: 556(67.2%) RA, 178(21.5%) SpA, 93(11.2%) Pso/PsA patients. Table 1 shows numbers, rates (per 100 person-years), and hazard ratio of discontinuation among biosimilar switchers compared with originator users. Figure 1 shows survival on treatment. The discontinuation rates for the biosimilar eternacept users was similar to the originator users (15.42 vs 15.63) per 100 PYs: HR (95% CI) 1.02 (0.87, 1.19 [p=0.718]). The biosimilar infliximab switchers had a slightly lower discontinuation rate than the originator users, however the difference in rate and risk of discontinuation were not statistically significant (8.76 vs 11.29) per 100 PYs: HR (95% CI) 0.85 (0.54, 1.36 [p=0.503]). <h3>Conclusion</h3> Population-based data on real-world experience mandating switching from originator to biosimilar etanercept and infliximab for IA revealed the biosimilar switchers have comparable duration of treatment to the original medications. <h3>Acknowledgements</h3> This research received funding from the Canadian Initiative for Outcomes in Rheumatology cAre (CIORA) via the Canadian Rheumatology Association. Dr. Lacaille is supported by the Mary Pack Chair in Arthritis Research from the University of British Columbia and The Arthritis Society of Canada. Dr. Antonio Avina Zubieta is a BC Lupus Society Research Scholar and a Walter &amp; Marilyn Booth Research Scholar. Dr. Hui Xie is supported by the Milan Ilich/ Merck Chair in Statistics for Arthritis and Musculoskeletal Diseases from Simon Fraser University. <h3>Disclosure of Interests</h3> None Declared.